HDL is thought to participate in reverse cholesterol transport by removing cholesterol from peripheral tissues and atherosclerotic lesions and directing its disposal to the liver. Our model of atherosclerosis employs use of the transformed human monocytic leukemic cell line, the THP-1 monocyte, which assumes macrophage morphology and function upon exposure to phorbol ester. Studies suggest that HDL-mediated cholesterol removal is modulated by changes in cell signal transduction. The time course for HDL removal of intracellular cholesterol suggests that the lipoprotein may effect protein synthesis and gene transcription. Our preliminary results indicate that THP-1 macrophages can accumulate esterified cholesterol (EC) when exposed to acetylated LDL (acLDL) with and without oleate. The specific aims of this research project are (1) To optimize the conditions for foam cell formation in the THP-1 macrophage; EC accumulation will be measured by mass and by incorporation of radiolabeled fatty acid into EC. (2) To investigate the role for cell signal transduction in HDL-mediated cholesterol clearance from THP-1 foam cells; Measurements will be performed for cAMP, adenylyl cyclase activity, G protein activation, protein kinase A activity, protein kinase C activity, diacylglycerol and inositol phosphate accumulation in cells exposed to control medium and that containing HDL. (3) To determine if HDL-mediated cholesterol clearance is associated with altered gene expression and protein synthesis; Appearance of newly synthesized gene products will be measured using the techniques of 2-D gel electrophoresis and differential plaque filter hybridization. Results from these studies will help to elucidate the mechanism(s) of HDL-mediated cholesterol removal from human macrophage foam cells. The Physician Scientist Award will allow the principal investigator to develop an expertise in the principles of cell and molecular biology in an environment well suited to this endeavor.